This project is an extension of previous work directed toward the study of noninvasive methods to determine spatial and temporal relationships existing between tissues of clinical interest. The approach involves in vitro modeling of promising systems and the development of prototypes suitable for clinical evaluation. Recent work has focused on studies directed toward development of versatile computerized radiographic system designed to be used both fluoroscopically and off-line to produce images which can be subtracted to show small changes in tissue occuring over long intervals of time, and combined in ways permitting tomographic display of specific slices of individual teeth. Feasibility has been demonstrated by creating tomosynthetic projections of the type obtainable from a tiny intraoral x-ray source having a movable focal spot which can be controlled electronically. Computer simulations also have shown that stabilization of projection geometry essential for subtraction radiography can be accommodated with the same rod-anode device. A rigorous theoretical analysis of unpredictable sources of variation confirms empirical observations that projection geometry rather than information capacity ultimately limits interproximal caries detectability. Other research anticipates faster computer hardware which would permit feed-back control of exposure and projection geometry in ways which would both improve image contrast and significantly reduce required exposure.